Yawei Kuang

Modeling and Design of Graphene GaAs Junction Solar Cell

Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work.

Trap-assisted tunneling in AlGaN avalanche photodiodes

We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

Two-Dimensional Modeling of Silicon Nanowires Radial Core-Shell Solar Cells

Silicon nanowires radial core-shell solar cells have recently attracted significant attention as promising candidates for low cost photovoltaic application, benefit from its strong light trapping, and short radial carrier collection distances. In order to establish optics and electricity improvement, a two-dimensional model based on Shockley-Read-Hall recombination modes has been carried out for radial core-shell junction nanowires solar cell combined with guided resonance modes of light absorption. The impact of SiNWs diameter and absorption layer thickness on device electrical performance based on a fixed nanowires height and diameter-over-periodicity were investigated under illumination. The variation in quantum efficiency indicated that the performance is limited by the mismatch between light absorption and carriers’ collection length.

Interface state density effect on the performance of graphene silicon heterojunction solar cell

A planar structure consisting of graphene layer as the hole transport material, and n-type silicon as substrate is simulated. The degradation of this cell caused by high interface state density has been carried out. The simulated results match published experimental results indicating the accuracy of the physics-based model. Using this model, the effect of interface state density as zero, 1×1016cm-2, 1×1017cm-2 on the photovoltaic performance has been studied. The obtained IV and EQE characteristic based on realistic parameters shows that the interface state playing a prominent role in graphene silicon schottky contact.

Numerical simulation study of graphene silicon solar cell with boron diffusion layer

Two dimensional model of graphene silicon heterojunction solar cell with an boron doped surface layer is structured using Silvaco TCAD tools by accurate control of diffusion process. The introduction of inverse doped layer obviously improved the efficiency of heterojunction photovoltaic cell.

Study on noise behaviors of epitaxial Si:P blocked-impurity-band detectors

The noise behaviors of the epitaxial Si:P BIB detectors have been investigated by experimental and theoretical tools. The device structure and testing system are presented in detail. The relationship between the noise spectral density and device temperature is analyzed. It is demonstrated that not only thermal noise but also shot noise are strongly dependent on the device temperature.

Light absorption enhancement by embedding aluminum nanodisk arrays in rear dielectric of ultra-thin film solar cells

In this work, in order to enhance the light absorption in one micron thick crystalline silicon solar cells, a back reflecting and plasmonic nanodisk scheme is proposed. We investigate the scattering properties of aluminum nanostructures located at the back side and optimize them for enhancing absorption in the silicon layer by using finite difference time domain simulations. The results indicate that the period and diameters nanoparticles, spacer layer have a strong impact on short circuit current enhancements. This finding could lead to improved light trapping within a thin silicon solar cell device.

Design consideration for ion-implanted planar GaAs blocked-impurity-band detectors

Design of ion implantation scheme for the planar GaAs blocked-impurity-band (BIB) detectors is performed by numerical simulation. The device structure and the preparation process are presented. It is demonstrated that the implanted Si ion concentration of the absorbing region and the contact region are 5×10¹⁵ cm^-3 and 4×10¹⁹ cm^-3, respectively, and can be implemented by four-step implantation with different ion energies and doses.

TCAD analysis of graphene silicon Schottky junction solar cell

The performance of graphene based Schottky junction solar cell on silicon substrate is studied theoretically by TCAD Silvaco tools. We calculate the current-voltage curves and internal quantum efficiency of this device at different conditions using tow dimensional model. The results show that the power conversion efficiency of Schottky solar cell dependents on the work function of graphene and the physical properties of silicon such as thickness and doping concentration. At higher concentration of 1e17cm-3 for n-type silicon, the dark current got a sharp rise compared with lower doping concentration which implies a convert of electron emission mechanism. The biggest fill factor got at higher phos doping predicts a new direction for higher performance graphene Schottky solar cell design.